Encoder, encoding method, decoder, and decoding method

ABSTRACT

An encoder that encodes a current block in a picture includes circuitry and memory. Using the memory, the circuitry: determines whether to use intra prediction for the current block; and when determining to use intra prediction, (i) performs a first transform on a residual signal of the current block using a first transform basis to generate first transform coefficients; and (ii-1) performs a second transform on the first transform coefficients using a second transform basis to generate second transform coefficients and quantizes the second transform coefficients, when an intra prediction mode of the current block is a predetermined mode or when the first transform basis is same as a predetermined transform basis; and (ii-2) quantizes the first transform coefficients without performing the second transform when the intra prediction mode is different from the predetermined mode and the first transform basis is different from the predetermined transform basis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/JP2018/026114 filed on Jul. 11, 2018,claiming the benefit of priority of U.S. Provisional Patent ApplicationNo. 62/532,116 filed on Jul. 13, 2017, the entire contents of which arehereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to encoding and decoding of animage/video on a block-by-block basis.

2. Description of the Related Art

A video coding standard known as High-Efficiency Video Coding (HEVC) isstandardized by the Joint Collaborative Team on Video Coding (JCT-VC).

SUMMARY

An encoder according to an aspect of the present disclosure is anencoder that encodes a current block in a picture. The encoder includes:circuitry; and memory. Using the memory, the circuitry: determineswhether to use intra prediction for the current block; when determiningto use intra prediction for the current block, (i) performs a firsttransform on a residual signal of the current block using a firsttransform basis to generate first transform coefficients; and (ii-1)performs a second transform on the first transform coefficients using asecond transform basis to generate second transform coefficients andquantizes the second transform coefficients, when an intra predictionmode of the current block is a predetermined mode or when the firsttransform basis is same as a predetermined transform basis; and (ii-2)quantizes the first transform coefficients without performing the secondtransform when the intra prediction mode of the current block isdifferent from the predetermined mode and the first transform basis isdifferent from the predetermined transform basis.

Note that these general or specific aspects may be implemented by asystem, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or by anycombination of systems, methods, integrated circuits, computer programs,or recording media.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1;

FIG. 2 illustrates one example of block splitting according toEmbodiment 1;

FIG. 3 is a chart indicating transform basis functions for eachtransform type;

FIG. 4A illustrates one example of a filter shape used in ALF;

FIG. 4B illustrates another example of a filter shape used in ALF;

FIG. 4C illustrates another example of a filter shape used in ALF;

FIG. 5A illustrates 67 intra prediction modes used in intra prediction;

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing;

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing;

FIG. 5D illustrates one example of FRUC;

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory;

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture;

FIG. 8 is for illustrating a model assuming uniform linear motion;

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks;

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode;

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing;

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing;

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1;

FIG. 11 is a flow chart illustrating transform and quantizationprocessing performed by an encoder according to Embodiment 2;

FIG. 12 is a flow chart illustrating inverse quantization and inversetransform processing performed by a decoder according to Embodiment 2;

FIG. 13 is a flow chart illustrating transform and quantizationprocessing performed by an encoder according to Embodiment 3;

FIG. 14 is a flow chart illustrating inverse quantization and inversetransform processing performed by a decoder according to Embodiment 3;

FIG. 15 is a flow chart illustrating transform and quantizationprocessing performed by an encoder according to Embodiment 4;

FIG. 16 is a flow chart illustrating inverse quantization and inversetransform processing performed by a decoder according to Embodiment 4;

FIG. 17 is a flow chart illustrating encoding processing performed by anencoder according to Embodiment 5;

FIG. 18 illustrates a specific example of syntax according to Embodiment5;

FIG. 19 is a flow chart illustrating decoding processing performed by adecoder according to Embodiment 5;

FIG. 20 is a flow chart illustrating encoding processing performed by anencoder according to Embodiment 6;

FIG. 21 is a flow chart illustrating decoding processing performed by adecoder according to Embodiment 6;

FIG. 22 illustrates an overall configuration of a content providingsystem for implementing a content distribution service;

FIG. 23 illustrates one example of an encoding structure in scalableencoding;

FIG. 24 illustrates one example of an encoding structure in scalableencoding;

FIG. 25 illustrates an example of a display screen of a web page;

FIG. 26 illustrates an example of a display screen of a web page;

FIG. 27 illustrates one example of a smartphone; and

FIG. 28 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(Underlying Knowledge Forming Basis of the Present Disclosure) Atwo-step frequency transform is proposed for blocks to which intraprediction is applied in Joint Exploration Test Model (JEM) software ofthe Joint Video Exploration Team (JVET). The two-step frequencytransform uses explicit multiple core transform (EMT) as the primarytransform and non-separable secondary transform (NSST) as the secondarytransform. The EMT adaptively selects a transform basis from among aplurality of transform bases to perform a transform from the spatialdomain to the frequency domain.

Such a two-step frequency transform has room for improvement in terms ofthe processing amount.

Hereinafter, embodiments based on such knowledge as described above willbe specifically described with reference to the drawings.

Note that the following embodiments describe general or specificexamples. The numerical values, shapes, materials, constituent elements,the arrangement and connection of the constituent elements, steps, theprocessing order of the steps, etc., illustrated in the followingembodiments are mere examples, and are not intended to limit the scopeof the claims. Moreover, among the constituent elements in the followingembodiments, those not recited in any one of the independent claimsrepresenting the most generic concepts will be described as optionalconstituent elements.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according toEmbodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1, encoder 100 is a device that encodes a pictureblock by block, and includes splitter 102, subtractor 104, transformer106, quantizer 108, entropy encoder 110, inverse quantizer 112, inversetransformer 114, adder 116, block memory 118, loop filter 120, framememory 122, intra predictor 124, inter predictor 126, and predictioncontroller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2, the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2, block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2, one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3, N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPL 1: H.265(ISO/IEC 23008-2 HEVC (High Efficiency Video Coding))).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6, in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7, in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8, (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v₁τ₀) and (−v_(x)τ₁, −v_(y)τ₁), respectively,and the following optical flow equation is given.

MATH. 1

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

$\begin{matrix}{{MATH}.\mspace{11mu} 2} & \; \\\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVR,processing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10, decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

Embodiment 2

Next, Embodiment 2 will be described. In an aspect of the presentembodiment, transform and inverse transform will be described in detail.Note that an encoder and a decoder according to the present embodimenthave substantially the same configurations as those of the encoder andthe decoder according to Embodiment 1. As such, the illustrations anddescriptions thereof will be omitted.

[Processing of Transformer and Quantizer of Encoder]

First, processing of transformer 106 and quantizer 108 of encoder 100according to the present embodiment will be specifically described withreference to FIG. 11. FIG. 11 is a flow chart illustrating transform andquantization processing performed by encoder 100 according to Embodiment2.

First, transformer 106 selects a first transform basis for a currentblock to be encoded from among one or more first transform basiscandidates (S101). For example, transformer 106 fixedly selects a DCT-IItransform basis as the first transform basis for the current block.Transformer 106 may select the first transform basis using an adaptivebasis selection mode, for example.

The adaptive basis selection mode is a mode in which a transform basisis adaptively selected from among a plurality of predetermined transformbasis candidates on the basis of a cost that is based on a code amountand/or the difference between an original image and a reconstructedimage. The adaptive basis selection mode is also referred as an EMT modeor an AMT mode. For example, the plurality of transform basesillustrated in FIG. 6 can be used as the plurality of transform basiscandidates. Note that the plurality of transform basis candidates arenot limited to the plurality of transform bases illustrated in FIG. 6.The plurality of transform basis candidates may include a transformbasis equivalent to no transform, for example.

By encoding, into a bitstream, identification information indicatingwhich of the adaptive basis selection mode and a fixed basis mode, inwhich a fixed transform basis (for example, the type-II DCT basis) isused, is enabled, it is possible to selectively use the adaptive basisselection mode and the fixed basis mode. The identification informationcorresponds to identification information indicating whether theadaptive basis selection mode is enabled. In such a case, there areinstances where the identification information allows determination asto whether the first transform basis is the same as a predeterminedtransform basis. For example, with the EMT, since there isidentification information (emt_cu_flag) indicating, in units such asCU, which of the adaptive basis selection mode and the fixed basis modeis enabled, it is possible to determine, using the identificationinformation, whether the first transform basis is the same as apredetermined transform basis.

Transformer 106 then performs a first transform on the residual of thecurrent block using the first transform basis selected in Step S101, soas to generate first transform coefficients (S102). The first transformcorresponds to the primary transform.

Transformer 106 determines whether the first transform basis selected inStep S101 is the same as a predetermined transform basis (S103). Forexample, transformer 106 determines whether the first transform basis isthe same as any one of the plurality of predetermined transform bases.Transformer 106 may determine whether the first transform basis is thesame as one predetermined transform basis, for example.

For example, a transform basis of the type-II DCT (i.e., DCT-II) and/ora similar transform basis can be used as the predetermined transformbasis. Such a predetermined transform basis may be predefined by astandard, for example. For example, the predetermined transform basismay be determined based on an encoding parameter or the like.

Here, when the first transform basis is the same as the predeterminedtransform basis (yes in S103), transformer 106 selects a secondtransform basis for the current block from among one or more secondtransform basis candidates (S104). Transformer 106 performs a secondtransform on the first transform coefficients using the second transformbasis selected, so as to generate second transform coefficients (S105).The second transform corresponds to the secondary transform. Quantizer108 quantizes the second transform coefficients generated (S106), andends the transform and quantization processing.

In the second transform, a secondary transform known as an NSST may beperformed, or a transform which selectively uses a second transformbasis among the plurality of second transform basis candidates may beperformed. At this time, in selecting a second transform basis, thetransform basis to be selected may be fixed. In other words, apredetermined fixed transform basis may be selected as the secondtransform basis. A transform basis equivalent to no second transform maybe used as the second transform basis.

The NSST may be a frequency-spatial transform following the DCT or DST.For example, the NSST may be Karhunen Loveve transform (KLT) performedon the transform coefficients of the DCT or DST obtained offline, orHypercube-Givens transform (HyGT) which represents a basis equivalent tothat of the KLT and is represented by a combination of rotationtransforms.

On the other hand, when the first transform basis is different from thepredetermined transform basis (no in S103), transformer 106 skips theselection of a second transform basis (S104) and the second transform(S105). In other words, transformer 106 does not perform the secondtransform. In such a case, the first transform coefficients generated inStep S102 are quantized (S106), and the transform and quantizationprocessing ends.

When the second transform is skipped as in the case above, informationindicating that the second transform is not performed may be notified tothe decoder. When the second transform is skipped, a second transformmay be performed using a second transform basis equivalent to notransform, and information indicating such a second transform basis maybe notified to the decoder.

Note that inverse quantizer 112 and inverse transformer 114 of encoder100 can reconstruct the current block by inversely performing theprocessing performed by transformer 106 and quantizer 108.

[Processing of Inverse Quantizer and Inverse Transformer of Decoder]

Next, processing of inverse quantizer 204 and inverse transformer 206 ofdecoder 200 according to the present embodiment will be specificallydescribed with reference to FIG. 12. FIG. 12 is a flow chartillustrating inverse quantization and inverse transform processingperformed by decoder 200 according to Embodiment 2.

First, inverse quantizer 204 inverse quantizes quantized coefficients ofa current block to be decoded (S601). Inverse transformer 206 determineswhether a first inverse transform basis for the current block is thesame as a predetermined inverse transform basis (S602). An inversetransform basis corresponding to the predetermined transform basis usedby encoder 100 is used as the predetermined inverse transform basis.

When the first inverse transform basis is the same as the predeterminedinverse transform basis (yes in S602), inverse transformer 206 selects asecond inverse transform basis for the current block (S603). To selectan inverse transform basis (the first inverse transform basis or thesecond inverse transform basis) in decoder 200 is to determine aninverse transform basis based on predetermined information. For example,a basis selection signal may be used as the predetermined information.An intra prediction mode or a block size, for example, can be used asthe predetermined information as well.

Inverse transformer 206 performs a second inverse transform on theinverse quantized coefficients of the current block using the secondinverse transform basis selected, so as to generate second inversetransform coefficients (S604). Further, inverse transformer 206 selectsa first inverse transform basis (S605). Using the first inversetransform basis selected, inverse transformer 206 performs a firstinverse transform on the second inverse transform coefficients generatedin S604 (S606), and ends the inverse quantization and inverse transformprocessing.

On the other hand, when the first inverse transform basis is differentfrom the predetermined inverse transform basis (no in S602), inversetransformer 206 skips the selection of a second inverse transform basis(S603) and the second inverse transform (S604). In other words, inversetransformer 206 does not perform the second inverse transform, andselects the first inverse transform basis (S605). Using the firstinverse transform basis selected, inverse transformer 206 performs thefirst inverse transform on the coefficients inverse quantized in S601(S606), and ends the inverse quantization and inverse transformprocessing.

[Advantageous Effects, Etc.]

The inventors have found the problem that the conventional encodinginvolves an enormous amount of processing in searching for an optimalcombination of a transform basis and a transform parameter (for example,filter coefficients) in both the first transform and the secondtransform. In contrast, encoder 100 and decoder 200 according to thepresent embodiment can skip the second transform according to the firsttransform basis. This results in reduction in the processing forsearching for an optimal combination of a transform basis and atransform parameter in both the first transform and the secondtransform, thus enabling reduction in the processing load whileinhibiting a decrease in the compression efficiency.

As described above, encoder 100 and decoder 200 according to the presentembodiment can skip the second transform when the first transform basisis different from a predetermined transform basis. First transformcoefficients generated through the first transform are affected by thefirst transform basis. Therefore, enhancement in the compression rateachieved through the second transform performed on the first transformcoefficients often depends on the first transform basis. As such, byskipping the second transform when the first transform basis isdifferent from a predetermined transform basis that leads to a greaterenhancement in the compression rate, it is possible to reduce theprocessing load while inhibiting a decrease in the compressionefficiency.

With the type-II DCT in particular, since transformed significantfrequency coefficients often concentrate in the low frequency band, theadvantageous effect of the second transform is likely to be greater. Inview of this, with use of the type-II DCT basis as the predeterminedtransform basis, the second transform is performed if enhancement in thecompression efficiency brought about by the second transform issignificant, and if not, the second transform is skipped. By doing so,reduction in the processing load is expected while inhibiting a furtherdecrease in the compression efficiency.

Note that the above processing is applicable to both a luma signal and achroma signal, and may be also applied to each signal of R, G, and Bwhen the input signal is in the RGB format. Moreover, bases that areselectable in the first transform or the second transform may bedifferent between the luma signal and the chroma signal. For example,the luma signal has a frequency band wider than the frequency band ofthe chroma signal. Thus, in the transform of the luma signal, more typesof bases may be selectable than in the transform of the chroma signal.

Note that the number of predetermined transform bases is not limited toone. That is to say, there may be a plurality of predetermined transformbases. In such a case, determination as to whether the first transformbasis is the same as any one of the plurality of transform bases issufficient.

Note that this aspect may be implemented in combination with one or moreof the other aspects according to the present disclosure. In addition,part of the processes in the flowcharts, part of the constituentelements of the apparatuses, and part of the syntax described in thisaspect may be implemented in combination with other aspects.

Embodiment 3

Next, Embodiment 3 will be described. An aspect of the presentembodiment is different from Embodiment 2 in that the transformprocessing differs depending on whether intra prediction is used for acurrent block to be encoded/decoded. Hereinafter, the present embodimentwill be described with reference to the drawings, focusing on thedifferences from Embodiment 2. Note that throughout the drawingsmentioned below, processing steps that are substantially the same asthose in Embodiment 2 are given the same reference numerals, andoverlapping descriptions will be omitted or simplified.

[Processing of Transformer and Quantizer of Encoder]

First, processing of transformer 106 and quantizer 108 of encoder 100according to the present embodiment will be specifically described withreference to FIG. 13. FIG. 13 is a flow chart illustrating transform andquantization processing performed by encoder 100 according to Embodiment3.

First, transformer 106 determines which of intra prediction and interprediction is to be used for a current block to be encoded (S201). Forexample, transformer 106 determines which of intra prediction and interprediction is to be used, on the basis of a cost that is based on a codeamount and/or the difference between an original image and areconstructed image obtained by locally decoding a compressed image. Forexample, transformer 106 may determine which of intra prediction andinter prediction is to be used, on the basis of information (forexample, the picture type) different from the cost that is based on thecode amount and/or the difference.

Here, when determining to use inter prediction for the current block(inter in S201), transformer 106 selects a first transform basis for thecurrent block from among one or more first transform basis candidates(S202). For example, transformer 106 fixedly selects a DCT-II transformbasis as the first transform basis for the current block. Transformer106 may select the first transform basis from among a plurality of firsttransform basis candidates, for example.

Transformer 106 then performs the first transform on the residual of thecurrent block using the first transform basis selected in Step S202, soas to generate first transform coefficients (S203). Quantizer 108quantizes the first transform coefficients generated (S204), and endsthe transform and quantization processing.

On the other hand, when determining to use intra prediction for thecurrent block (intra in S201), transformer 106 performs Steps S101through S105 in the same manner as in Embodiment 2. Then, quantizer 108quantizes the first transform coefficients generated in Step S102 or thesecond transform coefficients generated in Step S105 (S204), and endsthe transform and quantization processing.

[Processing of Inverse Quantizer and Inverse Transformer of Decoder]

Next, processing of inverse quantizer 204 and inverse transformer 206 ofdecoder 200 according to the present embodiment will be specificallydescribed with reference to FIG. 14. FIG. 14 is a flow chartillustrating inverse quantization and inverse transform processingperformed by decoder 200 according to Embodiment 3.

First, inverse quantizer 204 inverse quantizes quantized coefficients ofa current block to be decoded (S601). Inverse transformer 206 determineswhich of intra prediction and inter prediction is to be used for thecurrent block (S701). For example, inverse transformer 206 determineswhich of intra prediction and inter prediction is to be used, based oninformation obtained from a bitstream.

Here, when determining to use inter prediction for the current block(inter in S701), inverse transformer 206 selects a first inversetransform basis for the current block (S702). Using the first inversetransform basis selected in S702, inverse transformer 206 performs thefirst inverse transform on the inverse quantized coefficients of thecurrent block (S703), and ends the inverse quantization and inversetransform processing.

On the other hand, when determining to use intra prediction for thecurrent block (intra in S701), inverse transformer 206 performs StepsS602 through S606 in the same manner as in Embodiment 2, and ends theinverse quantization and inverse transform processing.

[Advantageous Effects, Etc.]

Encoder 100 and decoder 200 according to the present embodiment can skipthe second transform according to intra/inter prediction and the firsttransform basis. This results in reduction in the processing forsearching for an optimal combination of a transform basis and atransform parameter in both the first transform and the secondtransform, thus enabling reduction in the processing load whileinhibiting a decrease in the compression efficiency.

Note that this aspect may be implemented in combination with one or moreof the other aspects according to the present disclosure. In addition,part of the processes in the flowcharts, part of the constituentelements of the apparatuses, and part of the syntax described in thisaspect may be implemented in combination with other aspects.

Embodiment 4

Next, Embodiment 4 will be described. An aspect of the presentembodiment is different from Embodiments 2 and 3 in that the transformprocessing differs according to an intra prediction mode for a currentblock to be encoded/decoded. Hereinafter, the present embodiment will bedescribed with reference to the drawings, focusing on the differencesfrom Embodiments 2 and 3. Note that throughout the drawings mentionedbelow, processing steps that are substantially the same as those inEmbodiment 2 or 3 are given the same reference numerals, and overlappingdescriptions will be omitted or simplified.

[Processing of Transformer and Quantizer of Encoder]

First, processing of transformer 106 and quantizer 108 of encoder 100according to the present embodiment will be specifically described withreference to FIG. 15. FIG. 15 is a flow chart illustrating transform andquantization processing performed by encoder 100 according to Embodiment4.

In the same manner as in Embodiment 2, transformer 106 determines whichof intra prediction and inter prediction is to be used for a currentblock to be encoded (S201). Here, when determining to use interprediction for the current block (inter in S201), transformer 106performs Step S202 and Step S203 in the same manner as in Embodiment 2.Then, quantizer 108 quantizes the first transform coefficients generatedin Step S203 (S302).

On the other hand, when determining to use intra prediction for thecurrent block (intra in S201), transformer 106 performs Step S101 andStep S102 in the same manner as in Embodiment 1. Transformer 106 thendetermines whether the intra prediction mode for the current block is apredetermined mode (S301). For example, transformer 106 determineswhether the intra prediction mode is a predetermined mode on the basisof a cost that is based on a code amount and/or the difference betweenan original image and a reconstructed image. Note that the determinationas to whether the intra prediction mode is the predetermined mode may beperformed based on information different from the cost.

The predetermined mode may be predefined by a standard, for example. Thepredetermined mode may be determined based on an encoding parameter, forexample. For example, a directional prediction mode in a diagonaldirection can be used as the predetermined mode.

Directional prediction modes are intra prediction modes in which aparticular direction is used for predicting a current block. Indirectional prediction modes, pixel values are predicted by extendingthe values of reference pixels in a specific direction. Note that apixel value is the value of a pixel unit forming a picture, and is aluma value or a chroma value, for example. For example, directionalprediction modes are intra prediction modes excluding the DC predictionmode and the planar prediction mode.

Directional prediction modes in diagonal directions are directionalprediction modes each having a direction inclined with respect to thehorizontal and vertical directions. For example, the directionalprediction modes in diagonal directions may be, among directionalprediction modes in 65 directions identified by the numbers 2 through 66in order starting from the bottom left to the top right (see FIG. 5A),directional prediction modes in 3 directions identified by 2 (bottomleft), 34 (top left), and 66 (top right). In another example, thedirectional prediction modes in diagonal directions may be directionalprediction modes in 7 directions identified by 2 to 3 (bottom left), 33through 35 (top left), and 65 to 66 (top right) among the directionalprediction modes in the 65 directions.

When the intra prediction mode is not the predetermined mode (no inS301), transformer 106 determines whether the first transform basisselected in Step S101 is the same as a predetermined transform basis(S103).

When the intra prediction mode is the predetermined mode (yes in S301)or when the first transform basis is the same as the predeterminedtransform basis (yes in S103), transformer 106 selects a secondtransform basis for the current block from among one or more secondtransform basis candidates (S104). Transformer 106 performs the secondtransform on the first transform coefficients using the second transformbasis selected, so as to generate second transform coefficients (S105).Quantizer 108 quantizes the second transform coefficients generated(S302), and ends the transform and quantization processing.

When the intra prediction mode is different from the predetermined mode(no in S301) and the first transform basis is different from thepredetermined transform basis (no in S103), transformer 106 skips theselection of a second transform basis (S104) and the second transform(S105). In other words, transformer 106 does not perform the secondtransform. In such a case, the first transform coefficients generated inStep S102 are quantized (S302), and the transform and quantizationprocessing ends.

[Processing of Inverse Quantizer and Inverse Transformer of Decoder]

Next, processing of inverse quantizer 204 and inverse transformer 206 ofdecoder 200 according to the present embodiment will be specificallydescribed with reference to FIG. 16. FIG. 16 is a flow chartillustrating inverse quantization and inverse transform processingperformed by decoder 200 according to Embodiment 4.

First, inverse quantizer 204 inverse quantizes quantized coefficients ofa current block to be decoded (S601). Inverse transformer 206 determineswhich of intra prediction and inter prediction is to be used for thecurrent block (S701).

When determining to use inter prediction for the current block (inter inS701), inverse transformer 206 performs Step S702 and Step S703 in thesame manner as in Embodiment 3, and ends the inverse quantization andinverse transform processing.

On the other hand, when determining to use intra prediction for thecurrent block (intra in S701), inverse transformer 206 determineswhether the intra prediction mode for the current block is apredetermined mode (S801). The predetermined mode used in decoder 200 isthe same as the predetermined mode used in encoder 100.

When the intra prediction mode is not the predetermined mode (no inS801), inverse transformer 206 determines whether a first inversetransform basis for the current block is the same as a predeterminedinverse transform basis (S602).

When the intra prediction mode is the predetermined mode (yes in S801)or when the first inverse transform basis is the same as thepredetermined inverse transform basis (yes in S602), Steps S603 throughS606 are performed in the same manner as in Embodiment 2, and theinverse transform and inverse quantization processing ends.

On the other hand, when the intra prediction mode is different from thepredetermined mode (no in S801) and the first inverse transform basis isdifferent from the predetermined inverse transform basis (no in S602),inverse transformer 206 skips the selection of a second inversetransform basis (S603) and the second inverse transform (S604). In otherwords, inverse transformer 206 does not perform the second inversetransform, and selects a first inverse transform basis (S605). Using thefirst inverse transform basis selected, inverse transformer 206 performsthe first inverse transform on the coefficients inverse quantized inS601 (S606), and ends the inverse quantization and inverse transformprocessing.

[Advantageous Effects, Etc.]

As described above, encoder 100 and decoder 200 according to the presentembodiment can skip the second transform according to the intraprediction mode and the first transform basis. This results in reductionin the processing for searching for an optimal combination of atransform basis and a transform parameter in both the first transformand the second transform, thus enabling reduction in the processing loadwhile inhibiting a decrease in the compression efficiency.

In particular, when a directional prediction mode in a diagonaldirection is the predetermined mode, the second transform is performedif the directional prediction mode in a diagonal direction is used forthe current block, and if not, the second transform can be skipped. Thisenables reduction in the processing load while inhibiting a decrease inthe compression efficiency.

In the first transform, DCT or DST which is separable in the verticaldirection and the horizontal direction is generally performed. In such acase, the first transform does not use the correlation in diagonaldirections. Therefore, the first transform is not enough to sufficientlyaggregate coefficients when a directional prediction mode in a diagonaldirection having a high correlation in a diagonal direction is used. Inview of this, when a directional prediction mode in a diagonal directionis used for intra prediction, the second transform is performed using asecond transform basis which uses the correlation in a diagonaldirection. By doing so, it is possible to further aggregate thecoefficients and enhance the compression efficiency.

Note that the processing orders of the steps in the flow charts in FIG.15 and FIG. 16 are not limited to those illustrated in FIG. 15 and FIG.16. For example, in FIG. 16, the determination as to whether the intraprediction mode is the predetermined mode (S801) and the determinationas to whether the first transform basis is the same as the predeterminedtransform basis (S602) may be performed in reverse order or may beperformed simultaneously.

Note that this aspect may be implemented in combination with one or moreof the other aspects according to the present disclosure. In addition,part of the processes in the flowcharts, part of the constituentelements of the apparatuses, and part of the syntax described in thisaspect may be implemented in combination with other aspects.

Embodiment 5

Next, Embodiment 5 will be described. In an aspect of the presentembodiment, encoding/decoding of information regarding transform/inversetransform will be described. Hereinafter, the present embodiment will bedescribed with reference to the drawings, focusing on the differencesfrom Embodiments 2 through 4. Note that since transform and quantizationprocessing and inverse quantization and inverse transform processingaccording to the present embodiment are substantially the same as thosein Embodiment 4, the descriptions thereof will be omitted.

[Processing of Entropy Encoder of Encoder]

With reference to FIG. 17, the following specifically describes encodingprocessing for information regarding a transform performed by entropyencoder 110 of encoder 100 according to the present embodiment. FIG. 17is a flow chart illustrating encoding processing performed by encoder100 according to Embodiment 5.

When inter prediction is used for the current block (inter in S401),entropy encoder 110 encodes a first basis selection signal into abitstream (S402). Here, the first basis selection signal is informationor data indicating the first transform basis selected in Step S202 inFIG. 15.

To encode a signal into a bitstream is to place a code indicatinginformation in a bitstream. The code is generated by context-basedadaptive binary arithmetic coding (CABAC), for example. Note that thecode need not always be generated using CABAC or entropy encoding. Forinstance, the code may be the information itself (a flag of 0 or 1, forexample).

Next, entropy encoder 110 encodes coefficients quantized in Step S302 inFIG. 15 (S403), and ends the encoding processing.

When intra prediction is used for the current block (intra in S401),entropy encoder 110 encodes, into a bitstream, an intra prediction modesignal indicating the intra prediction mode for the current block(S404). Entropy encoder 110 further encodes a first basis selectionsignal into the bitstream (S405). Here, the first basis selection signalis information or data indicating the first transform basis selected inStep S101 illustrated in FIG. 15.

Here, when the second transform has been performed (yes in S406),entropy encoder 110 encodes a second basis selection signal into thebitstream (S407). Here, the second basis selection signal is informationor data indicating the second transform basis selected in Step S104. Onthe other hand, when the second transform is not performed (no in S406),entropy encoder 110 skips the encoding of the second basis selectionsignal (S407). That is to say, entropy encoder 110 does not encode thesecond basis selection signal.

Lastly, entropy encoder 110 encodes coefficients quantized in Step S302(S408), and ends the encoding processing.

[Syntax]

FIG. 18 illustrates a specific example of syntax according to Embodiment5.

In FIG. 18, a prediction mode signal (pred_mode), an intra predictionmode signal (pred_mode_dir), and an adaptive selection mode signal(emt_mode), and, as necessary, a first basis selection signal(primary_transform_type) and a second basis selection signal(secondary_transform_type) are encoded into a bitstream.

The prediction mode signal (pred_mode) indicates which of intraprediction and inter prediction is to be used for a current block to beencoded/decoded (here, a coding unit). Based on the prediction modesignal, inverse transformer 206 of decoder 200 can determine whether touse intra prediction for the current block.

The intra prediction mode signal (pred_mode_dir) indicates an intraprediction mode for when intra prediction is to be used for a currentblock to be encoded/decoded. Based on the intra prediction mode signal,inverse transformer 206 of decoder 200 can determine whether the intraprediction mode for the current block is a predetermined mode.

The adaptive selection mode signal (emt_mode) indicates whether to use,for a current block to be encoded/decoded, an adaptive basis selectionmode in which a transform basis is adaptively selected from among aplurality of transform basis candidates. Here, when the adaptiveselection mode signal is “ON”, a transform basis is selected from amongthe type-V DCT, the type-VIII DCT, the type-I DST, and the type-VII DST.On the other hand, when the adaptive selection mode signal is “OFF”, thetype-II DCT is selected. Based on the adaptive selection mode signal,inverse transformer 206 of decoder 200 can determine whether the firstinverse transform basis of the current block is the same as apredetermined inverse transform basis.

The first basis selection signal (primary_transform_type) indicates afirst transform basis/inverse transform basis used for atransform/inverse transform of a current block to be encoded/decoded.The first basis selection signal is encoded into a bitstream when theadaptive selection mode signal is “ON”. On the other hand, when theadaptive selection mode signal is “OFF”, the first basis selectionsignal is not encoded. Inverse transformer 206 of decoder 200 can selecta first inverse transform basis based on the first basis selectionsignal.

The second basis selection signal (secondary_transform_type) indicates asecond transform basis/inverse transform basis used for atransform/inverse transform of a current block to be encoded/decoded.The second basis selection signal is encoded into a bitstream when theadaptive selection mode signal is “ON” and the intra prediction modesignal is “2”, “34”, or “66”. The intra prediction mode signals “2”,“34”, and “66” each indicate a directional prediction mode in a diagonaldirection. That is to say, the second basis selection signal is encodedinto a bitstream when the first transform basis is the same as the typeII DCT basis and the intra prediction mode is a directional predictionmode in a diagonal direction. On the other hand, the second basisselection signal is not encoded into a bitstream when the intraprediction mode is not a directional prediction mode in a diagonaldirection. Inverse transformer 206 of decoder 200 can select a secondinverse transform basis based on the second basis selection signal.

Note that here, the bases of the type-V DCT, the type-VIII DCT, thetype-I DST, and the type-WI DST are used as transform bases selectablein the adaptive basis selection mode; however, the present disclosure isnot limited to these. For example, the type-IV DCT may be used insteadof the type-V DCT. Since the type-IV DCT can partially use theprocessing of the type-II DCT, the processing load can be reduced.Furthermore, the type-IV DST may be used. Since the type-IV DST canpartially use the processing of the type-IV DCT, the processing load canbe reduced.

[Processing of Entropy Decoder of Decoder]

Next, processing of entropy decoder 202 of decoder 200 according to thepresent embodiment will be specifically described with reference to FIG.19. FIG. 19 is a flow chart illustrating decoding processing performedby decoder 200 according to Embodiment 5.

When inter prediction is to be used for a current block to be decoded(inter in S901), entropy decoder 202 decodes a first basis selectionsignal from a bitstream (S902).

To decode a signal from a bitstream is to parse a code indicatinginformation from a bitstream, and to reconstruct the information fromthe parsed code. The reconstruction from the code to the information isperformed using context-based adaptive binary arithmetic decoding(CABAD), for example. Note that the reconstruction from the code to theinformation need not always be performed using CABAD or entropydecoding. For instance, parsing of the mere code is sufficient when theparsed code itself indicates the information (a flag of 0 or 1, forexample).

Next, entropy decoder 202 decodes the quantized coefficients from thebitstream (S903), and ends the decoding processing.

When intra prediction is to be used for the current block (intra inS901), entropy decoder 202 decodes an intra prediction mode signal froma bitstream (S904). Entropy decoder 202 further decodes a first basisselection signal from the bitstream (S905).

Here, when the second inverse transform is to be performed (yes inS906), entropy decoder 202 decodes a second basis selection signal fromthe bitstream (S907). On the other hand, when the second inversetransform is not to be performed (no in S906), entropy decoder 202 skipsthe decoding of the second basis selection signal (S907). That is tosay, entropy decoder 202 does not decode the second basis selectionsignal.

Lastly, entropy decoder 202 decodes the quantized coefficients from thebitstream (S908), and ends the decoding processing.

[Advantageous Effects, Etc.]

As described above, encoder 100 and decoder 200 according to the presentembodiment can encode the first basis selection signal and the secondbasis selection signal into a bitstream. By encoding the intraprediction mode signal and the first basis selection signal prior to thesecond basis selection signal, it is possible to determine, prior todecoding the second basis selection signal, whether to skip the secondinverse transform. Accordingly, in the case of skipping the secondinverse transform, it is possible to skip the encoding of the secondbasis selection signal as well, and thus the compression efficiency canbe enhanced.

Embodiment 6

Next, Embodiment 6 will be described. An aspect of the presentembodiment is different from Embodiment 5 in that information indicatingan intra prediction mode in which the second transform is performed isencoded. Hereinafter, the present embodiment will be described withreference to the drawings, focusing on the differences from Embodiment5. Note that throughout the drawings mentioned below, processing stepsthat are substantially the same as those in Embodiment 5 are given thesame reference numerals, and overlapping descriptions will be omitted orsimplified.

[Processing of Entropy Encoder of Encoder]

With reference to FIG. 20, the following specifically describes encodingprocessing for information regarding a transform performed by entropyencoder 110 of encoder 100 according to the present embodiment. FIG. 20is a flow chart illustrating encoding processing performed by encoder100 according to Embodiment 6.

When inter prediction is used for a current block to be encoded (interin S401), entropy encoder 110 performs Step S402 and Step S403 in thesame manner as in Embodiment 5, and ends the encoding processing.

On the other hand, when intra prediction is used for the current block(intra in S401), entropy encoder 110 encodes a second transform targetprediction mode signal into a bitstream (S501). The second transformtarget prediction mode signal indicates a predetermined mode fordetermining whether to perform the second inverse transform.Specifically, the second transform target prediction mode signalindicates an intra prediction mode number (2, 34, or 66, for example),for instance.

Note that the unit of coding for the second transform target predictionmode signal may be a coding unit (CU) or a coding tree unit (CTU), ormay be a sequence parameter set (SPS), a picture parameter set (PPS), ora slice unit corresponding to H.265/HEVC standard.

After that, entropy encoder 110 performs Steps S404 through S408 in thesame manner as in Embodiment 5, and ends the encoding processing.

[Processing of Entropy Decoder of Decoder]

Next, processing of entropy decoder 202 of decoder 200 according to thepresent embodiment will be specifically described with reference to FIG.21. FIG. 21 is a flow chart illustrating decoding processing performedby decoder 200 according to Embodiment 6.

When inter prediction is to be used for a current block to be decoded(inter in S901), entropy decoder 202 performs Step S902 and Step S903 inthe same manner as in Embodiment 5, and ends the decoding processing.

On the other hand, when intra prediction is to be used for the currentblock (intra in S901), entropy decoder 202 decodes a second transformtarget prediction mode signal from a bitstream (S1001).

After that, entropy encoder 202 performs Steps S904 through S908 in thesame manner as in Embodiment 5, and ends the decoding processing.

[Advantageous Effects, Etc.]

As described above, encoder 100 and decoder 200 according to the presentembodiment can encode, into a bitstream, the second transform targetprediction mode signal indicating a predetermined mode that is the intraprediction mode in which the second transform/inverse transform isperformed. Accordingly, the predetermined mode can be freely determinedon the encoder 100 side, and the compression efficiency can be enhanced.

Note that the order in which the signals are encoded may be determinedin advance, and various signals may be encoded in an order differentfrom the aforementioned encoding order.

Note that this aspect may be implemented in combination with one or moreof the other aspects according to the present disclosure. In addition,part of the processes in the flowcharts, part of the constituentelements of the apparatuses, and part of the syntax described in thisaspect may be implemented in combination with other aspects.

Embodiment 7

Various modifications may be made to Embodiments 2 through 6.

For example, in each of the above embodiments, the first transform basismay be fixed according to the size of the current block to beencoded/decoded. For instance, when the block size is smaller than acertain size (for example, 4×4 pixels, 4×8 pixels, or 8×4 pixels), thefirst transform basis may be fixed to a type-VII DST transform basis,and at this time, encoding of the first basis selection signal may beskipped.

Furthermore, for example, in each of the above embodiments, a signal maybe encoded which indicates whether to enable the processing of skippingthe selection of the first transform basis and the first transform orthe selection of the second transform basis and the second transform.For example, when the processing of skipping the second transform isenabled, the second basis selection signal may not be encoded, and thus,the decoding operation becomes different from the decoding operationperformed when the processing of skipping the second transform isdisabled. The unit of coding for such a signal may be a coding unit (CU)or a coding tree unit (CTU), or may be a sequence parameter set (SPS), apicture parameter set (PPS), or a slice unit corresponding to H.265/HEVCstandard.

For example, in each of the above embodiments, the selection of thefirst transform basis and the first transform may be skipped, or theselection of the second transform basis and the second transform may beskipped, based on the picture type (I, P, B), the slice type (I, P, B),the block size, the number of non-zero coefficients, a quantizationparameter, or Temporal_id (layer of hierarchical coding).

Note that when the encoder performs such operations as described above,the decoder also performs corresponding operations. For example, whenthe information indicating whether to enable the processing of skippingthe first transform or second transform is encoded, the decoder decodesthat information to determine whether the first or second transform isenabled and whether the first or second basis selection signal isencoded.

Note that in Embodiments 5 and 6, a plurality of signals (for example,the intra prediction mode signal, the adaptive selection mode signal,the first basis selection signal, and the second basis selection signal)are encoded into a bitstream; however, in Embodiments 2 through 4, thesesignals need not be encoded into a bitstream. For example, these signalsmay be notified from encoder 100 to decoder 200 separately from thebitstream.

Note that in the present embodiment, the respective positions, in thebitstream, of the plurality of signals (for example, the intraprediction mode signal, the adaptive selection mode signal, the firstbasis selection signal, and the second basis selection signal) are notparticularly limited. The plurality of signals are encoded into at leastone of a plurality of headers, for example. For example, a videoparameter set, a sequence parameter set, a picture parameter set, and aslice header can be used as the plurality of headers. Note that when asignal is located in two or more layers (for example, a pictureparameter set and a slice header), the signal in a lower layer (forexample, the slice header) overwrites the signal in a higher layer (forexample, the picture parameter set).

Embodiment 8

As described in each of the above embodiments and variations, eachfunctional block can typically be realized as an MPU and memory, forexample. Moreover, processes performed by each of the functional blocksare typically realized by a program execution unit, such as a processor,reading and executing software (a program) recorded on a recordingmedium such as ROM. The software may be distributed via, for example,downloading, and may be recorded on a recording medium such assemiconductor memory and distributed. Note that each functional blockcan, of course, also be realized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments andvariations may be realized via integrated processing using a singleapparatus (system), and, alternatively, may be realized viadecentralized processing using a plurality of apparatuses. Moreover, theprocessor that executes the above-described program may be a singleprocessor or a plurality of processors. In other words, integratedprocessing may be performed, and, alternatively, decentralizedprocessing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and variations and asystem that employs the same will be described. The system ischaracterized as including an image encoder that employs the imageencoding method, an image decoder that employs the image decodingmethod, and an image encoder/decoder that includes both the imageencoder and the image decoder. Other configurations included in thesystem may be modified on a case-by-case basis.

Usage Examples

FIG. 22 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments and variations on still-image or video content captured by auser via the terminal, multiplexes video data obtained via the encodingand audio data obtained by encoding audio corresponding to the video,and transmits the obtained data to streaming server ex103. In otherwords, the terminal functions as the image encoder according to oneaspect of the present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 23, that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments and variations. The server may have a configuration inwhich content is switched while making use of the temporal and/orspatial scalability of a stream, which is achieved by division into andencoding of layers, as illustrated in FIG. 23. Note that there may be aplurality of individual streams that are of the same content butdifferent quality. In other words, by determining which layer to decodeup to based on internal factors, such as the processing ability on thedecoder side, and external factors, such as communication bandwidth, thedecoder side can freely switch between low resolution content and highresolution content while decoding. For example, in a case in which theuser wants to continue watching, at home on a device such as a TVconnected to the internet, a video that he or she had been previouslywatching on smartphone ex115 while on the move, the device can simplydecode the same stream up to a different layer, which reduces serverside load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 24, metadata is stored usinga data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 25 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 26 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 25 and FIG. 26, a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

Other Usage Examples

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments and variations may be implemented in a digital broadcastingsystem. The same encoding processing and decoding processing may beapplied to transmit and receive broadcast radio waves superimposed withmultiplexed audio and video data using, for example, a satellite, eventhough this is geared toward multicast whereas unicast is easier withcontent providing system ex100.

[Hardware Configuration]

FIG. 27 illustrates smartphone ex115. FIG. 28 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments and variations, a video signal storedin memory ex467 or a video signal input from camera ex465, and transmitsthe encoded video data to multiplexer/demultiplexer ex453. Moreover,audio signal processor ex454 encodes an audio signal recorded by audioinput unit ex456 while camera ex465 is capturing, for example, a videoor still image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodimentsand variations, and video or a still image included in the linked movingpicture file is displayed on display ex458 via display controller ex459.Moreover, audio signal processor ex454 decodes the audio signal andoutputs audio from audio output unit ex457. Note that since real-timestreaming is becoming more and more popular, there are instances inwhich reproduction of the audio may be socially inappropriate dependingon the user's environment. Accordingly, as an initial value, aconfiguration in which only video data is reproduced, i.e., the audiosignal is not reproduced, is preferable. Audio may be synchronized andreproduced only when an input, such as when the user clicks video data,is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, and digital video cameras, etc.

What is claimed is:
 1. An encoder that encodes a current block in apicture, the encoder comprising: circuitry; and memory, wherein usingthe memory, the circuitry: determines whether to use intra predictionfor the current block; when determining to use intra prediction for thecurrent block, (i) performs a first transform on a residual signal ofthe current block using a first transform basis to generate firsttransform coefficients; and (ii-1) performs a second transform on thefirst transform coefficients using a second transform basis to generatesecond transform coefficients and quantizes the second transformcoefficients, when an intra prediction mode of the current block is apredetermined mode or when the first transform basis is same as apredetermined transform basis; and (ii-2) quantizes the first transformcoefficients without performing the second transform when the intraprediction mode of the current block is different from the predeterminedmode and the first transform basis is different from the predeterminedtransform basis.
 2. The encoder according to claim 1, wherein thepredetermined mode is a directional prediction mode in a diagonaldirection.
 3. The encoder according to claim 1, wherein thepredetermined transform basis is a type-II discrete cosine transformbasis.
 4. The encoder according to claim 1, wherein whether the firsttransform basis is same as the predetermined transform basis isdetermined based on identification information that indicates whether anadaptive basis selection mode is enabled, the adaptive basis selectionmode being a mode in which a first transform basis is adaptivelyselected from among a plurality of first transform basis candidates. 5.An encoding method for encoding a current block in a picture, theencoding method comprising: determining whether to use intra predictionfor the current block; when determining to use intra prediction for thecurrent block, (i) performing a first transform on a residual signal ofthe current block using a first transform basis to generate firsttransform coefficients; and (ii-1) performing a second transform on thefirst transform coefficients using a second transform basis to generatesecond transform coefficient and quantizing the second transformcoefficients, when an intra prediction mode of the current block is apredetermined mode or when the first transform basis is same as apredetermined transform basis; and (ii-2) quantizing the first transformcoefficients without performing the second transform when the intraprediction mode of the current block is different from the predeterminedmode and the first transform basis is different from the predeterminedtransform basis.
 6. A decoder that decodes a current block in a picture,the decoder comprising: circuitry; and memory, wherein using the memory,the circuitry: determines whether to use intra prediction for thecurrent block; and when determining to use intra prediction for thecurrent block, (i-1) performs a second inverse transform on inversequantized coefficients of the current block using a second inversetransform basis to generate second inverse transform coefficients andperforms a first inverse transform on the second inverse transformcoefficients using a first inverse transform basis, when an intraprediction mode of the current block is a predetermined mode or when thefirst inverse transform basis used in the first inverse transform of thecurrent block is same as a predetermined inverse transform basis; and(i-2) performs the first inverse transform on the inverse quantizedcoefficients of the current block using the first inverse transformbasis without performing the second inverse transform, when the intraprediction mode of the current block is different from the predeterminedmode and the first inverse transform basis is different from thepredetermined inverse transform basis.
 7. The decoder according to claim6, wherein the predetermined mode is a directional prediction mode in adiagonal direction.
 8. The decoder according to claim 6, wherein thepredetermined inverse transform basis is a type-II discrete cosinetransform basis.
 9. The decoder according to claim 6, wherein whetherthe first inverse transform basis is same as the predetermined inversetransform basis is determined based on identification information thatindicates whether an adaptive basis selection mode is enabled, theadaptive basis selection mode being a mode in which a first transformbasis is adaptively selected from among a plurality of first transformbasis candidates.
 10. A decoding method for decoding a current block ina picture, the decoding method comprising: determining whether to useintra prediction for the current block; and when determining to useintra prediction for the current block, (i-1) performing a secondinverse transform on inverse quantized coefficients of the current blockusing a second inverse transform basis to generate second inversetransform coefficients and performing a first inverse transform on thesecond inverse transform coefficients using a first inverse transformbasis, when an intra prediction mode of the current block is apredetermined mode or when the first inverse transform basis used in thefirst inverse transform of the current block is same as a predeterminedinverse transform basis; and (i-2) performing the first inversetransform on the inverse quantized coefficients of the current blockusing the first inverse transform basis without performing the secondinverse transform, when the intra prediction mode of the current blockis different from the predetermined mode and the first inverse transformbasis is different from the predetermined inverse transform basis.